Experimental Study On Degradation Of Oxytetracycline By Centrifugal Pump Hydraulic Cavitation

In recent years,antibiotics have been frequently detected in many watersheds in China,which has great potential harm to the natural environment and human health.Because the traditional water treatment methods are difficult to meet the environmental protection requirements of degrading oxytetracycline（OTC）pollutants in water,it is very necessary to study new water treatment technologies.Centrifugal pump hydraulic cavitation technology,as an advanced oxidation technology with simple equipment operation,green pollution-free and low energy consumption,has attracted extensive attention.In this paper,by using the self-made centrifugal pump hydraulic cavitation device,the five influencing factors of solution pH（pH=3,5,7,9 and 11）,initial concentration of oxytetracycline（1 mg/L,3 mg/L,5 mg/L,7 mg/L and 9 mg/L）,reaction time（0～8 h）,solution temperature（25℃,30℃,35℃,40℃and 45℃）and outlet pressure of centrifugal pump（0.10MPa,0.15 MPa,0.20 MPa,0.25 MPa and 0.30 MPa）were experimentally studied;The mineralization degree,degradation mechanism and possible intermediate products in the process of hydraulic cavitation degradation of oxytetracycline by centrifugal pump were analyzed by means of total organic carbon,UV-vis spectrophotometer and liquid chromatography-mass spectrometry;According to the existing research results,hydrogen peroxide（H₂O₂）,chlorine dioxide（Cl O₂）,potassium persulfate（K₂S₂O₈）and sodium hypochlorite（Na Cl O）were selected to enhance the hydraulic cavitation degradation of oxytetracycline by centrifugal pump;To explore the experimental study on the effects of oxidant enhanced centrifugal pump hydraulic cavitation reaction time（0～8 h）,solution pH（pH=3,5,7,9 and 11）and centrifugal pump outlet pressure（0.10 MPa,0.15 MPa,0.20 MPa,0.25 MPa and 0.30 MPa）on the degradation rate of oxytetracycline.Finally,through the combination of box Behnken design（BBD）and response surface method（RSM）,establish a model for typical influencing factors（oxidant dosage,operation time and outlet pressure）,optimize the test conditions and explore the test results.The following are the main conclusions of this paper:（1）The degradation rate of oxytetracycline is 27.85%when the solution pH=3,the outlet pressure of centrifugal pump is 0.25 MPa,the initial concentration of oxytetracycline is1 mg/L and the reaction time is 3 h.The optimum degradation temperature of the solution is40℃.（2）In the process of degrading oxytetracycline,·OH radical plays a major role,the solution is mineralized,and the difference of degradation rate between different absorption peaks is small,which proves that all parts of oxytetracycline are destroyed almost at the same time,the degradation process is synchronous,and the mass spectrum peak of oxytetracycline m/z=460.4 disappears,new typical substances appear,and macromolecular substances are degraded into small molecular substances.（3）The degradation rates of centrifugal pump hydraulic cavitation combined with Na Cl O,Cl O₂,H₂O₂and K₂S₂O₈for 3 hours were 71.03%,77.45%,80.13%and 76.31%respectively.The four oxidants can enhance the degradation effect,and there is the best dosage of H₂O₂and K₂S₂O₈.Degradation effect under the conditions of equal molar amount:centrifugal pump hydraulic cavitation+H₂O₂>centrifugal pump hydraulic cavitation+Cl O₂>centrifugal pump hydraulic cavitation+K₂S₂O₈>centrifugal pump hydraulic cavitation+NaClO.The comparison test shows that H₂O₂+centrifugal pump hydraulic cavitation is an ideal method to degrade oxytetracycline wastewater.（4）The degradation of oxytetracycline by centrifugal pump hydraulic cavitation and combined H₂O₂conforms to the first-order kinetic equation at 0～3 h and the second-order kinetic equation at 0～8 h.Centrifugal pump hydraulic cavitation+H₂O₂,pH=3 and centrifugal pump outlet pressure of 0.25 MPa are the best conditions.Through the response surface method,the optimal test conditions are H₂O₂dosage of 0.3 L,centrifugal pump outlet pressure of 0.26 MPa and reaction time of 189.23 min.There is little difference between the predicted degradation rate and the actual value,and the model is reliable.